Main Features of General Oceanic Circulation and their Physical Exploration IQTl 



to a period of about 2 weeks and a wavelength of about 6000 km. The force producing 

 them thus has the form fFsin (Ix + vt ), where W is about 1 cm^ sec"^; for an east- 

 wards movement of the disturbance v is negative. For periods of 1-7 weeks — values 

 which are comparable with the periods of barotropic Rossby waves — the ocean 

 reacts largely as a homogeneous water body. As the period increases the baroclinic 

 effects become also larger and for longer periods (more than a year) the motion is 

 only partly barotropic and the baroclinic effects will be more important. For very long 

 wind-periods (at least about 100 years) the motion is entirely baroclinic. The flow is 

 geostrophic and in full accord with a stationary state. 



The second type of wind-driven ocean currents is that produced by a stationary 

 wind field imposed suddently at a given time. In this case all the possible free waves of 

 the system may develop and an investigation can be made of the relative importance 

 of inertial-gravitational waves and of geostrophically balanced motions. 



If the action of the wind lasts for a period comparable with that of an ordinary storm 

 then the geostrophically balanced motion will be partly barotropic and partly baro- 

 clinic. The internal boundary surface also reacts on the wind influence and this effect 

 can definitely be found (10-20 m), if the wind continues for 3 or more days. The deep 

 currents, however, remain weak and are probably no stronger than the thermo-haline 

 currents such as those produced by Antarctic cooling. The effect of storms can thus 

 make little contribution to the large-scale lateral mixing inside the oceanic stratosphere. 



Other movements of inertia and gravitational character which may be generated 

 are stronger but are not accompanied by measurable displacements of the boundary 

 surface ; they are pure horizontal inertia oscillations without any horizontal pressure 

 gradients and depend largely on the earth rotation. 



These investigations of Veronis and Stommel are undoubtedly of great import- 

 ance for a knowledge of the dynamics of the ocean currents. They are, of course, so far 

 incomplete; they do not, for instance, provide an explanation for the effects of 

 barriers (coasts and the sea bottom) as well as for the effects of friction. At the 

 present time, however, it is sufficient to gain some insight into the time-variable 

 action of the wind. This is all the more important because of the extreme difficulty of 

 gaining an insight into such rapidly changing phenomena solely by means of oceano- 

 graphic observations. 



